The present invention relates to improvements in a wave spring and particularly to improvements in a wave spring or imparting a linear weight versus deflection characteristic to a wave spring component.
A wave spring formed by winding a steel band having a flat cross section into a coil to serve as a spring structure is known. As shown in FIG. 10, a wave spring 1 has predetermined numbers of ridges 2 and troughs 3 per turn circumferentially disposed at a predetermined pitch such that the upper end of a ridge in one coil layer is opposed to the lower end of said trough in an adjacent coil layer thus forming a spring structure.
The coil shape of the said wave spring 1 is selected such that the magnitude of a deflection S produced when the wave spring 1 is subjected to an axial compression load P lies in a predetermined region of elastic deformation of the spring material, e.g. steel. For example, in the case where said wave spring is used in a clutch device of a speed changer for automobiles, it is desirable that a linear or substantially linear deformation characteristic be maintained between the load P imposed on the wave spring 1 by depressing the clutch pedal and the deflection S produced by said load, at least in its effective operation region.
FIG. 11 is a load versus deflection diagram for explaining by way of example said deformation characteristic. In the initial region I where the compression load P is started to be applied to the wave spring, the load versus deflection characteristic is unstable since the ridges 2 and the troughs 3 in the upper stage contact each other or since the clearance between the ridge 2 and the trough 3 of the wave spring varies in size. In contrast, in the terminal load region III, the ridges 2 and troughs 3 of the wave spring approach the closely contacted state, whereby the load P sharply increases with little change in deflection. Actually, the wave spring 1 functions as a spring structure in which the relation between the load P and the deflection S is maintained nearly linear only in the intermediate region II which is the effective operation region of the spring.
In this connection, heretofore used as a factor which determines the coil shape of the wave spring 1 is a deformation sine curve (TMS), shown in FIG. 13 (A) or a deformation trapezoid curve shown in FIG. 13 (B).
FIG. 12 is a perspective view showing a deflection measuring instrument 6 prepared fox measuring the elastic characteristics of the wave spring 1, with the wave spring 1 placed thereon. A wave spring, for example, the wave spring 1 whose coil shape is determined by the deformation sine curve (TMS), is seated on the deflection measuring instrument 6 and the deflection H produced by a distributed compression load P is measured. The deflection measuring instrument 6 is a spring structure support block comprising a pair of spring support flanges 4 disposed on opposite sides radially extending from a center point O, and a spring support surface 5 in the form of a sectorial planar plate which is connected to the inner lateral surfaces of the support flanges 4. In use, the wave spring 1 is positioned with its opposite ends abutting against the inner lateral surfaces of the support flanges 4 and a distributed compression load P is imposed on the center of the ridge 2 to measure the elastic deformation S produced in the wave spring 1.
The wave spring 1 experiences a decrease in the height H of the ridge 2 above the spring support surface 5 with the imposition of the distributed compression load P, and simultaneously therewith, the ends of the troughs 3 are slid along the inner lateral surfaces of the spring support flanges 4, resulting in a radially outwardly directed (indicated by the reference character R) diameter increasing movement. By measuring the amount of sink, i.e., elastic deformation H, of the ridge 2 while progressively increasing the distributed compression load P, a load versus deflection curve as shown in FIG. 11 is obtained.
As will be understood from the above description, if the coil shape of the wave spring 1 is designed to be a modified sine curve or modified trapezoid, the load versus deflection curve will be appreciably nonlinear even in the intermediate region II which is designed to be the effective operating region, as shown in FIG. 11. In the case where deflection v. load linearity is not retained in such linear load versus deflection characteristic, the width of selection of spring characteristics is narrowed, presenting such problems as an increase in the number of design steps and an increase in the characteristic testing period. As a result, deflection v. load linearity is no longer retained between load and deflection as in the clutch of an automobile speed changer having the wave spring 1 incorporated therein and, furthermore, the number of design steps is increased by repetition of trial making of wave springs; thus, the manufacturing cost of wave springs increases greatly.